Portable apparatus for cutting vegetation are well known in the art. Such apparatus generally comprise a heat engine or an electric engine at the end of a shaft. The engine, located at the vicinity of a handle, drives in rotation at a high speed of generally about several thousand rounds per minute. A cutting head holds one or a plurality of cutting strings. The one or the plurality of cutting strings extend more or less radially with respect to the axis of rotation under the effect of centrifugal force when the cutting head is driven in rotation. There are essentially two kinds of cutting heads having a locking element of the cutting string. A first kind of cutting head includes a reel receiving a cutting string wound to the reel, where the cutting string progressively winds off the reel as the cutting string wears away.
The second kind of cutting head includes a locking element of one or a plurality of cutting strings of short length.
The locking element that holds the cutting string onto the cutting head usually comprises one or a plurality of string strand passageways formed by metallic or similar eyelets mounted on a peripheral surface of the head. It is through these passageways that respective strands of string emerge from the head. The strand of string comprises a stop. Besides a high production cost induced by the stop, it is difficult to replace the cutting string onto the cutting head described above in the course of use because the user is generally wearing gloves.
To overcome this drawback, various locking elements for use with a cutting string have been proposed.
Most of these locking elements of the cutting string strand comprise a moving locking element, such as a cam, which is urged by a spring and/or by the centrifugal force generated during rotation of the head so as to exert pressure on the string. A supporting backing wall may be provided opposite the locking element in order to hold the string locally captive between the element and the supporting wall. Examples of locking elements are shown and described in U.S. Pat. Nos. 4,301,642 and 4,355,510, as well as European Patent No. EP 0824854. To improve the locking effect, it is also known to provide the locking element with a series of teeth capable of anchoring better in the material of the string, which is generally made of polyamide. U.S. Pat. No. 6,928,741 and European Patent No. EP 1416786 show a locking element comprising a cam provided with teeth and cooperating with a spring.
The teeth provide a better locking effect when used with a smooth cutting string strand, but are inoperative when used with a toothed cutting string as disclosed in European Patent Appln. No. EP 1422990, filed by the applicant and marketed under the Trademark Flexiblade©.
One of the objects of the invention is thus to remedy these drawbacks by proposing a cutting head for a brush cutter, edge trimmer, or similar comprising at least one cutting string strand passageway and a locking element of said cutting string of simple design, low cost and achieving the locking of smooth and/or toothed cutting string strand.